Roll-supporting mandrels of variable length are standard items in a number of installations. Most of these devices have telescoping components that are spring-biased to increase length for insertion and removal from support brackets that have peripherally-closed bearing sections. In other words, insertion into the bracket requires a shortening of the mandrel against the action of an internal compression spring to a sufficient degree to permit insertion between the brackets, followed by axial extension by the spring as the unit snaps into the bearing recesses in the brackets. Probably the most common application of such a device is in the toilet roll bracket.
A quite different type of application for a variable-length mandrel is found in the support of a roll of paper in a calculating machine. In this case, one or both of the spaced bracket sections have a radially-open bearing permitting the mandrel to be lifted out directly, rather than shortened for axial withdrawal from the bearing recesses. The standardization of the width of the paper rolls results in a corresponding approximate standardization of the spacing between the bracket sections, but each manufacturer tends to prefer its own selected bearing diameter. The removable mandrels tend to be lost over the periods of use of the calculating machines, and suppliers and service personnel have found it necessary to stock a wide assortment of such mandrels in order to supply the needs of the users of the machines made by the various manufacturers. The usual spring-loaded mandrel of the type common in conjunction with toilet roll brackets is not convenient in the calculating machine application, for a number of reasons. One of these is that it is undesirable to have a continuing end thrust operating on the support brackets of the calculator, as many of these are merely relatively thin-walled structures of molded plastic material which exhibit a tendency toward deformation under continued pressure. The standard form of the spring-loaded mandrel would also serve no particular purpose, as no provision is made for accommodating the mandrel to varying diameters of the bearing sections that are in common use. In the calculator application, there is no particular advantage to a variable axial length except to engage different journal diameters, as the spacing between the bracket sections is fairly standard.